A fluorine-containing adhesive and a silicone adhesive have been known as an adhesive having heat resistance to 200° C. or higher. A fluorine-containing adhesive is an adhesive that has the best heat resistance, but has a problem that it is considerably expensive. A silicone adhesive is used in widespread fields since it is inexpensive and is excellent in heat resistance, but has a problem that it generates siloxane gas, which causes insulation failure, upon exposing to a high environmental temperature of 250° C. or higher for a prolonged period of time. A silicone adhesive having been used includes a peroxide curing type and an addition reaction curing type. A peroxide curing type silicone adhesive uses an organic peroxide, such as benzoyl peroxide and the like, as a curing agent, and requires a high temperature of 150° C. or higher for curing, as a result, the use thereof involves a problem that it is difficult to apply to a substrate that has poor heat resistance. An addition reaction curing type silicone adhesive undergoes crosslinking through addition reaction of an SiH group and an alkenyl group with a platinum catalyst (see, for example, Patent Document 1), and can be cured at a low temperature, whereby it is suitable for applying to a substrate that is poor in heat resistance. However, the adhesive causes gradual progress of the addition reaction and decrease in amount of the SiH group as a crosslinking agent through the consumption thereof in the processing solution before applying to the substrate, thereby suffers from the problems such that not only the adhesion characteristics are fluctuated, but also increase in viscosity or gelation of the processing solution is caused, and the curing property of the adhesive is lowered, in any case, the adhesive is not cured at all, with the lapse of time. There is a demand in market for a heat resistant adhesive that is of lower cost than the fluorine-containing adhesive and is not deteriorated even at a high temperature of 250° C., but it is the current situation that no sufficiently satisfactory product has been obtained.
A polyimide resin has been widely used as engineering plastics excellent in heat resistance, and in particular, a polyimide resin obtained by reacting a bismaleimide compound and an aromatic diamine as raw materials is being widely used as a thermosetting polyimide resin for an electric insulating material and the like.
It is known that a cured product of a thermosetting polyimide resin formed with polyoxyalkylene bismaleimide, which is an aliphatic bismaleimide, an aromatic bismaleimide and an aromatic diamine as raw materials has not only heat resistance but also adhesiveness (see, for example, Patent Document 2).
However, such a high temperature as 150° C. or higher is required for obtaining the cured product by reacting a bismaleimide compound and an aromatic diamine, and thus there is the similar problem that it is difficult to apply to a substrate that has poor heat resistance.
[Patent Document 1] JP-B-54-37907
[Patent Document 2] U.S. Pat. No. 4,116,937